Refractive index

The refractive index is a physical property that indicates the factor by which the wavelength and the phase velocity of light in a particular material are reduced compared with a vacuum.

This reduction causes light rays to be refracted when they pass from one medium into another, which, for example, in lenses leads to the focusing of light or in prisms to the splitting of light into its spectral colours. In optics, the refractive index plays a central role, as it determines how strongly light rays are bent on entering a medium and how this affects the optical properties of materials.